X-ray lithography is a proximity patterning technique. A gold pattern X-ray mask is used to selectively absorb and transmit soft X-rays for exposing a resist-coated wafer held in close proximity to the mask. The X-ray mask itself comprises a thin substrate of BN, SiC, or Ti that is supported by a rigid mounting ring. The gold mask absorber pattern is formed by etching a 7000 angstrum thick, gold film deposited on the substrate or by a special, low stress gold plating process.
Soft seven angstrum X-rays are generated by a high-power source, a water-cooled rotating anode and an electron gun located together in a vacuum chamber. X-rays are generated by focusing the hollow, coned-shaped beam of electrons onto the rotating tungsten surface of the anode. The cylindrical, high-powered electron gun allows the X-rays generated in a small diameter spot to pass through it. This diverging cone of X-ray radiation then passes through a thin beryllium vacuum window into a helium filled exposure chamber. The mask and wafer are closely aligned prior to insertion into the exposure chamber, and maintained during exposure.
While mask ring assemblies heretofore proposed met with reasonable success, the present invention is directed to improvements in such systems, as will be become apparent as the description proceeds.
Related patents in this field include inter alia: U.S. Pat. No. 3,743,842 issued July 3, 1973; U.S. Pat. No. 3,892,973 issued July 1, 1975; U.S. Pat. No. 4,037,111 issued July 19, 1977; U.S. Pat. No. 4,085,329 issued Apr. 18, 1978; U.S. Pat. No. 4,185,202 issued Jan. 22, 1980; U.S. Pat. No. 4,187,431 issued Feb. 5, 1980; U.S. Pat. No. 4,215,192 issued July 29, 1980; U.S. Pat. No. 4,238,682 issued Dec. 9, 1980; U.S. Pat. No. 4,301,237 issued Nov. 17, 1981 and U.S. Pat. No. 4,335,313 issued Jan. 15, 1982.